SpringBoot3 自定义 Starter

SpringBoot3 自定义 Starter

SpringBoo3 最简单自定义 Starter 步骤。
1. 启动一个空白模板项目

gradle或者maven项目
引入如下依赖:

1. implementation("org.springframework.boot:spring-boot-autoconfigure:3.5.0")

复制代码

2. 手写自动配置类

1. package edu.tyut.config
3. import org.slf4j.Logger
4. import org.slf4j.LoggerFactory
5. import org.springframework.beans.factory.BeanFactory
6. import org.springframework.boot.autoconfigure.AutoConfiguration
7. import org.springframework.boot.autoconfigure.AutoConfigurationPackages
8. import org.springframework.context.annotation.Bean
10. private const val BASE_PACKAGE: String = "basePackage"
12. /**
13. * custom config
14. */
15. @AutoConfiguration
16. internal open class CustomAutoConfig {
17.     private val logger: Logger = LoggerFactory.getLogger(this.javaClass)
18.     @Bean(value = [BASE_PACKAGE])
19.     internal open fun getBasePackage (
20.         beanFactory: BeanFactory
21.     ): String {
22.         val packages: List<String> = AutoConfigurationPackages.get(beanFactory)
23.         logger.info("CustomAutoConfig AutoConfiguration Packages: $packages")
24.         return packages.firstOrNull() ?: "edu.tyut"
25.     }
26. }

复制代码

3. 注册自动配置类

在文件resources/META-INF/spring/org.springframework.boot.autoconfigure.AutoConfiguration.imports下注册:

1. edu.tyut.config.CustomAutoConfig

复制代码

End, 怎么样是不是非常简单

原理解析

1. 启动类的注解@SpringBootApplication

源码如下：

1. @Target(ElementType.TYPE)
2. @Retention(RetentionPolicy.RUNTIME)
3. @Documented
4. @Inherited
5. @SpringBootConfiguration
6. @EnableAutoConfiguration
7. @ComponentScan(excludeFilters = { @Filter(type = FilterType.CUSTOM, classes = TypeExcludeFilter.class),
8.                 @Filter(type = FilterType.CUSTOM, classes = AutoConfigurationExcludeFilter.class) })
9. public @interface SpringBootApplication {
10. ...
11. }

复制代码

2. @EnableAutoConfiguration

源码如下：

1. @Target(ElementType.TYPE)
2. @Retention(RetentionPolicy.RUNTIME)
3. @Documented
4. @Inherited
5. @AutoConfigurationPackage
6. @Import(AutoConfigurationImportSelector.class)
7. public @interface EnableAutoConfiguration {
8. ...
9. }

复制代码

3. AutoConfigurationImportSelector

源码如下：

1. public class AutoConfigurationImportSelector implements DeferredImportSelector, BeanClassLoaderAware,
2.                 ResourceLoaderAware, BeanFactoryAware, EnvironmentAware, Ordered {
3.         private final Class<?> autoConfigurationAnnotation;
4.         AutoConfigurationImportSelector(Class<?> autoConfigurationAnnotation) {
5.                 this.autoConfigurationAnnotation = (autoConfigurationAnnotation != null) ? autoConfigurationAnnotation
6.                                 : AutoConfiguration.class;
7.         }
8. ...
9.         protected List<String> getCandidateConfigurations(AnnotationMetadata metadata, AnnotationAttributes attributes) {
10.                 ImportCandidates importCandidates = ImportCandidates.load(this.autoConfigurationAnnotation,
11.                                 getBeanClassLoader());
12.                 List<String> configurations = importCandidates.getCandidates();
13.                 Assert.state(!CollectionUtils.isEmpty(configurations),
14.                                 "No auto configuration classes found in " + "META-INF/spring/"
15.                                                 + this.autoConfigurationAnnotation.getName() + ".imports. If you "
16.                                                 + "are using a custom packaging, make sure that file is correct.");
17.                 return configurations;
18.         }
19. ...
20. }

复制代码

代码解读
查看该类构造函数可以发现其有一个成员变量autoConfigurationAnnotation,其值为org.springframework.boot.autoconfigure.AutoConfiguration.
getCandidateConfigurations的参数为即为org.springframework.boot.autoconfigure.AutoConfiguration.
4. org.springframework.boot.context.annotation.ImportCandidates

源码如下：

1. public final class ImportCandidates implements Iterable<String> {
2. ...
3.         public static ImportCandidates load(Class<?> annotation, ClassLoader classLoader) {
4.                 Assert.notNull(annotation, "'annotation' must not be null");
5.                 ClassLoader classLoaderToUse = decideClassloader(classLoader);
6.                 String location = String.format(LOCATION, annotation.getName());
7.                 Enumeration<URL> urls = findUrlsInClasspath(classLoaderToUse, location);
8.                 List<String> importCandidates = new ArrayList<>();
9.                 while (urls.hasMoreElements()) {
10.                         URL url = urls.nextElement();
11.                         importCandidates.addAll(readCandidateConfigurations(url));
12.                 }
13.                 return new ImportCandidates(importCandidates);
14.         }
15. }

复制代码

代码解读:
找到类路径下所有的META-INF/spring/full-qualified-annotation-name.imports文件，读取内容（自动配置类的全限定名）, 如果在自动配置类没有org.springframework.boot.autoconfigure.AutoConfiguration注解，会抛出IllegalArgumentException异常。
META-INF/spring/full-qualified-annotation-name.imports文件 -> URL -> BufferedReader -> ImportCandidates.
5. ImportCandidates

ImportCandidates包含了所有的自动配置类，SpringBoot会对其进行进一步的处理。

End 本文分享结束， 有什么不足还请大家指出

来源：程序园用户自行投稿发布，如果侵权，请联系站长删除
免责声明：如果侵犯了您的权益，请联系站长，我们会及时删除侵权内容，谢谢合作！